Compute the Brier score.
The smaller the Brier score, the better, hence the naming with “loss”.
Across all items in a set N predictions, the Brier score measures the
mean squared difference between (1) the predicted probability assigned
to the possible outcomes for item i, and (2) the actual outcome.
Therefore, the lower the Brier score is for a set of predictions, the
better the predictions are calibrated. Note that the Brier score always
takes on a value between zero and one, since this is the largest
possible difference between a predicted probability (which must be
between zero and one) and the actual outcome (which can take on values
of only 0 and 1). The Brier loss is composed of refinement loss and
calibration loss.
The Brier score is appropriate for binary and categorical outcomes that
can be structured as true or false, but is inappropriate for ordinal
variables which can take on three or more values (this is because the
Brier score assumes that all possible outcomes are equivalently
“distant” from one another). Which label is considered to be the positive
label is controlled via the parameter pos_label, which defaults to 1.
Read more in the User Guide.

Parameters:

y_true:array, shape (n_samples,)

True targets.

y_prob:array, shape (n_samples,)

Probabilities of the positive class.

sample_weight:array-like of shape = [n_samples], optional

Sample weights.

pos_label:int or str, default=None

Label of the positive class. If None, the maximum label is used as
positive class